ANSWER AND EXPLANATION:The correct answer is CExplanation: Core Characteristics and Use-Related Characteristics are the two sub-principles of WBS Quality Principle 1. These principles are explained in the PMI practice standard for WBS. NOTE: This is probably one of the most obscure types of questions you will encounter on practice exams or on the actual PMP Exam. The PMI actually published a document separate from the PMBOK Guide titled "WBS Quality Principles", which outlines the suggested guidelines to use when performing the Create WBS process. Please refer to this document (available at www.pmi.org) for more detailed information.Reference: PMI Practice Standard for WBS 2nd Edition, page 19